1. Field of the Invention
The present invention relates to an in-plane switching (IPS) liquid crystal display (LCD) having a structure for changing a bright pixel to a dark pixel and a method of changing a bright pixel to a dark pixel.
2. Description of Related Art
An LCD is used in various types of electronic equipment such as a personal computer and a cellular phone. Among various LCDs, an IPS LCD is used as a wide viewing angle LCD.
As shown in FIG. 1(a), an IPS LCD 40 comprises a pixel region 12, an aperture 14 formed in the pixel region in which liquid crystal and strip-like pixel electrodes 16 are provided, a CS (capacitor storage) circuit 18 adjacent to the aperture 14, and a pad 20 disposed in opposition to the CS circuit 18 and connected to the pixel electrodes 16. A CS line in a pixel region 12 is referred to as the “CS circuit”. A storage capacity is thus formed by the pad and CS circuit. A TFT (thin film transistor) 24 is used as a switching element for connecting the signal line 26 and the pad 20. A gate line 22 of the TFT 24 is provided in parallel with the CS line. The pixel regions 12 are arranged in rows and columns on a substrate. To the aperture 14, common electrodes 28 are provided in parallel with the pixel electrodes 16. A potential of the common electrode 28 is the earth potential. Arbitrary numbers of the pixel electrodes 16 and the common electrodes 28 can be used, since electric fields are generated between the pixel electrodes 16 and the common electrodes 28.
In the IPS LCD 40, an electric field 44 is generated between the pixel electrode 16 and the common electrode 28 by applying a voltage to the pixel electrode 16, as shown in FIG. 1(b). A display is created by controlling the orientation of liquid crystal molecules 42 by this electric field 44. In this specification, the IPS LCD 40 is a normally black display. Therefore, the pixel 12 is dark when no voltage is applied to the pixel electrode 16, whereas it is bright when voltage is applied thereto.
In the IPS LCD 40, a short circuit between the signal line 26 and the pixel electrode 16, a short circuit between a drain electrode and a source electrode of the TFT 24, or a short circuit between a gate electrode and a drain electrode of the TFT 24 causes a bright pixel defect. Such bright pixel has higher intensity than a normal pixel when the LCD is on or off and significantly degrades the display quality of the LCD.
In order to solve the above problem, a method of changing a bright pixel to a dark pixel has been conventionally employed so as to obscure the bright pixel defect. In this method, the pad 20 and the CS circuit 18 are short-circuited by the application of laser beam so as to equalize the potentials of the electrodes 16 and the CS circuit 18. In this specification, the dark pixel means a black pixel regardless of whether the LCD is on or off.
However, in order to short-circuit members consisting mainly of aluminum, high-energy laser beam must be applied. This may cause the meltdown of the aluminum members, heat transfer to the liquid crystal, and the generation of bubbles in and around the aperture 14.
Further, Japanese Unexamined Patent Publication No. (Patent Kokai No.) 11-119253 (1999) discloses a transformed gate line and a method of cutting a gate line of a bright pixel by laser. However, since aluminum or tantalum is used as a gate line, the cutting of the gate line may exert an adverse effect on surrounding pixels as described above.
Accordingly, an object of the present invention is to provide an IPS LCD having a structure for changing a bright pixel to a dark pixel and a method of changing a bright pixel to a dark pixel.